At the very moment he cried out, David realised that what he had run into was only the Christmas tree. Disgusted with himself at such cowardice, he spat a needle from his mouth, stepped back from the tree and listened. There were no sounds of any movement upstairs: no shouts, no sleepy grumbles, only a gentle tinkle from the decorations as the tree had recovered from the collision.

Then, after a smoky-burnout to warm up the tires, you're lined up next to another competitor and the Christmas tree lights blink down... yellow, yellow, yellow, green!

(oil industry jargon) The collection of valves sometimes found at the top of a working oil well.

2011, Robert Heidersbach, Metallurgy and Corrosion Control in Oil and Gas Production, ISBN0470248483, page 232:

Wellheads, which support downhole tubing, casing, and other components, are connected at the top of wells to Christmas trees, which control production rates and fluid flows out of the well and may also direct fluids and equipment into the well

(bodybuilding) A pattern of muscles visible in the lower back, resembling in outline the shape of a conifer.